Phthalides are prevalent in biologically active compounds and natural products. In addition, these heterocycles can serve as versatile building blocks for the synthesis of natural and pharmaceutically-important products. So, efforts have been dedicated to the development of new methodologies to prepare 3,3′-disubstituted phthalide derivatives. However, many of these methods are non-convergent synthetic routes and rely on intramolecular cyclization, requiring relatively complex syntheses of the starting materials in order to bring diversity to the final phthalides. In the past few years, our laboratory has been focusing on developing chemistry using bimetallic ate complexes composed of a polar organometallic (e.g. an organolithium) and a “soft” organometallic (organomagnesium for example) in metal halogen exchange (MHE) reaction. Based on that expertise, we decided to started a research program with the aim of exploring the reactivity of organomagnesiates for the synthesis of substituted phthalides. Thereby, we showed that BIPHEN-based monobutylmagnesiate ((rac)-BIPHENBuMgLi where (rac)-BIPHEN is (rac)-5,5',6,6'-tetramethyl-3,3'-dit-butyl-1,1'-biphenyl-2,2'-diol) can efficiently promote the MHE of easily available 2-iodobenzoate derivatives, followed by addition of a ketone which lead to an intramolecular cyclisation, and the formation of a series of new diversely 3,3’-disubstituted isobenzofuranones in good yield. Among the several MHE agents investigated, (rac)-(BIPHEN)BuMgLi was the only one to make such a process possible with full tolerance of various reactive functional substituents useful for subsequent transformations. The synthetic pathway to access the magnesiate has been found to play a prominent role in its reactivity. Therefore, the bimetallic magnesiate complex has been characterized by solution-state 1H, 7Li and 1H DOSY NMR experiments.